Method of mixing fluids using a valve

ABSTRACT

A thermostatic mixing valve for the mixing of a first fluid and a second fluid is disclosed. The thermostatic mixing valve is configured to produce a mixed fluid of a particular temperature from a first fluid of a temperature higher than or equal to the particular temperature and a second fluid of a temperature lower than or equal to the particular temperature. The thermostatic mixing valve includes a valve body having a first fluid inlet, a second fluid inlet, and a mixed fluid outlet. The thermostatic mixing valve also includes a valve member configured to control the rate of flow of at least the first fluid. The valve member includes a thermostatic control device in communication with the mixed fluid and a shuttle coupled to the thermostatic control device, configured for movement within a liner, and oriented to adjustably engage the flow of at least the first fluid through at least one opening within a wall of the liner, the direction of flow of the first fluid being at least partially transverse with respect to the shuttle. At least one fluid inlet may include a check valve configured to prevent fluid from flowing out of the valve through the inlet. The check valve includes a first check valve member which is stationary, a second check valve member which is movable and engageable with the first check valve member, and a spring for urging the second check valve member into engagement with the first check valve member and for defining the path of motion of the second check valve member.

RELATED APPLICATION

The present application is a continuation application of a U.S. patentapplication Ser. No. 10/378,185 entitled. “METHOD OF MIXING FLUIDS IN AVALVE” filed Mar. 3, 2003 now U.S. Pat. No. 6,851,400, which is acontinuation application of then co-pending U.S. Pat. No. 6,543,478 U.S.application Ser. No. 09/941,141 entitled. “THERMOSTATIC MIXING VALVE”filed Aug. 28, 2001, which is a divisional application of then U.S.patent application Ser. No. 09/633,728 now U.S. Pat. No. 6,315,210entitled, “THERMOSTATIC MIXING VALVE” filed Aug. 7, 2000, which is acontinuation of then U.S. patent application Ser. No. 09/165,880entitled, “THERMOSTATIC MIXING VALVE” filed Oct. 2, 1998 now abandoned,which applications are hereby expressly incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to a thermostatic mixing valve.

BACKGROUND OF THE INVENTION

Thermostatic mixing valves are known for the producing of a mixed fluidby combining the supplies of a first (relatively hot) fluid and of asecond (relatively cold) fluid. Known arrangements for thermostaticmixing valves generally include a first fluid inlet, a second fluidinlet, a mixed fluid outlet, a mixing chamber, and a thermostaticcontrol device. Known thermostatic mixing valves generally vary the flowrate of at least the first fluid and often also of the second fluid, thetemperatures, pressures, and flow rates of both of which are typicallynot known and may vary randomly during operation, to produce a mixedfluid of a substantially constant temperature.

It would be advantageous to provide for a thermostatic mixing valve toallow relatively high flow rates of first, second, and mixed fluidswhile incurring only relatively moderate pressure drops within thethermostatic mixing valve. It would also be advantageous for athermostatic mixing valve to automatically shut off flow of at least ahot fluid upon failure of the thermostatic control device. It wouldfurther be advantageous to provide for a thermostatic mixing valve whichallows for relatively high flow rates with only moderate pressure dropsand which shuts off flow of at least the hot fluid.

SUMMARY OF THE INVENTION

The present invention relates to a thermostatic mixing valve configuredto produce a mixed fluid substantially of a particular temperature fromthe mixing of a first fluid of a temperature higher than or equal to theparticular temperature and of a second fluid of a temperature lower thanor equal to the particular temperature. The thermostatic mixing valveincludes a valve body having a first fluid inlet, a second fluid inlet,and a mixed fluid outlet. The thermostatic mixing valve also includes avalve member configured to control the rate of flow of at least thefirst fluid. The valve member includes a thermostatic control device incommunication with the mixed fluid and a shuttle coupled to thethermostatic control device, configured for movement within a liner, andoriented to adjustably engage the flow of at least the first fluidthrough at least one opening within a wall of the liner, the directionof movement of the shuttle with respect to the liner defining the majorlongitudinal axis of the thermostatic mixing valve, the direction offlow of the first fluid being at least partially transverse with respectto the major longitudinal axis of the valve.

The present invention also relates to a thermostatic mixing valveconfigured to produce a mixed fluid substantially of a particulartemperature from a first fluid of a temperature higher than or equal tothe particular temperature and a second fluid of a temperature lowerthan or equal to the particular temperature. The thermostatic mixingvalve includes a valve body having a first fluid inlet, a second fluidinlet, and a mixed fluid outlet, and a valve member configured tocontrol the rate of flow of the first fluid and the rate of flow of thesecond fluid. The valve member includes a thermostatic control device incommunication with the mixed fluid and a shuttle coupled to thethermostatic control device, configured for movement within a liner, andoriented to adjustably engage in opposing relationship the flow of thefirst fluid and the flow of the second fluid, the direction of movementof the shuttle with respect to the liner defining the major longitudinalaxis of the thermostatic mixing valve, the directions of flow of thefirst fluid and the second fluid being at least partially transversewith respect to the major longitudinal axis of the thermostatic mixingvalve.

The present invention further relates to a mixing valve configured toproduce a mixed fluid from the mixing of a first fluid and at least asecond fluid. The mixing valve includes a valve body having a firstfluid inlet, at least a second fluid inlet, and a fluid outlet, and atleast one fluid inlet including a check valve configured to preventfluid from flowing out of the valve through the at least one inlet. Thecheck valve includes a first check valve member which is stationarywithin and with respect to the valve body, a second check valve memberwhich is movable within the valve body in a defined path of motion andengageable with the first check valve member, and a biasing device forurging the second check valve member into engagement with the firstcheck valve member and for defining the path of motion of the secondcheck valve member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a thermostatic mixing valve according toa preferred embodiment of the present invention.

FIG. 2 is an exploded perspective view of the thermostatic mixing valveof FIG. 1.

FIG. 3 is a front sectional elevation view of the thermostatic mixingvalve of FIG. 3.

FIG. 3A is a fragmentary elevation view of the thermostatic mixing valveof FIG. 3.

FIG. 4A is a front sectional elevation view of the thermostatic mixingvalve of FIG. 1 showing full cold fluid flow and partial hot fluid flow.

FIG. 4B is a front sectional elevation view of the thermostatic mixingvalve of FIG. 1 showing cold fluid flow.

FIG. 4C is a front sectional elevation view of the thermostatic mixingvalve of FIG. 1 showing full flow of both hot fluid and cold fluid.

FIG. 4D is front sectional elevation view of the thermostatic valve ofFIG. 1 showing the thermostat having failed and flow of only cold fluid.

FIG. 5 is a front elevation view of the thermostatic mixing valveaccording to an alternative embodiment.

FIG. 6 is a left side elevation view of the thermostatic mixing valve ofFIG. 5.

FIG. 7 is a front sectional elevation view of the thermostatic mixingvalve of FIG. 5.

FIG. 7A is a fragmentary elevation view of the thermostatic mixing valveof FIG. 7.

FIG. 8A is a front sectional elevation view of the thermostatic mixingvalve of FIG. 5 showing flow of both hot fluid and cold fluid.

FIG. 8B is a front sectional elevation view of the thermostatic mixingvalve of FIG. 5 showing flow of only cold fluid.

FIG. 8C is a front sectional elevation view of the thermostatic mixingvalve of FIG. 5 showing flow of only hot fluid.

FIG. 8D is a front sectional elevation view of the thermostatic mixingvalve of FIG. 5 showing the thermostat having failed and no fluid flow.

FIG. 9 is an exploded perspective view of the thermostatic mixing valveof FIG. 5.

FIG. 10 is an exploded perspective view of a valve member of thethermostatic mixing valve of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 through 4 show a thermostatic mixing valve according to apreferred embodiment for producing from a first fluid and a second fluida mixed fluid substantially of a particular temperature which isintermediate the temperatures of the first fluid and the second fluid.The first fluid is higher in temperature than is the second fluid. Forease of understanding, the first fluid is sometimes referred to hereinas a hot fluid and the second fluid as a cold fluid (though both may be“hot” or “cold” in terms of human sensory perception and they may beseparated by only a relatively small temperature difference).

FIG. 1 shows a thermostatic mixing valve 102 having a valve body 104, acold fluid inlet port 110 associated with a cold fluid inlet designatedby the reference letter “C”, a hot fluid inlet port 112 associated witha hot fluid inlet designated by the reference letter “H”, and a mixedfluid outlet port 114 associated with a mixed fluid outlet designated bythe reference letter “M”. Thermostatic mixing valve 102 also includes abonnet 116, a cap 134, and a cover screw 142 for limiting access to anadjusting screw 140 (shown in FIG. 2). Thermostatic mixing valve 102further includes a first check valve 274 associated with hot fluid inletH and a second check valve 274 associated with cold fluid inlet C, eachcheck valve 274 including a check valve cap 276 in which is threadedlyengaged a stem 286.

FIG. 2 shows valve body 104 including cold fluid inlet port 110, hotfluid inlet port 112, and mixed fluid outlet port 114. Ports 110, 112,and 114 are configured for the connecting and seating of appropriatefluid conduits (e.g., using pipe threads) to valve body 104. A checkvalve 274 is assembled to valve body 104 in association with each inletport 110 and 112. Check valve 274 includes a seat 284, a plug 282, acheck valve cap 276, a stem 286, a cylindrical filter screen 279, and abiasing spring 280. Check valve cap 276 is provided with threads 294 forengagement with threaded aperture 296 within valve body 104, and issealed to valve body 104 with an annular seal 278. Stem 286 is providedwith threads 290 for engagement with a threaded aperture 292 centrallylocated within check valve cap 276, and is sealed to check valve cap 276by an annular seal 285.

Valve body 104 further includes a cavity 106 for the receiving of avalve member 144. Valve body 104, valve cap 134, adjusting screw 140,and cover screw 142 may be made of various materials. According to anyparticularly preferred embodiment, valve body 104 and valve cap 134 arecast of brass, gray iron, or ductile iron, and adjusting screw 140 andcover screw 142 are machined of brass, bronze, or stainless steel.

A liner 146 is configured generally as a hollow cylinder having a sidewall 152 and a lower end closed by a bottom wall 150 (shown in FIG. 3).Liner 146 further includes at least one transversely oriented upperopening 154 and at least one transversely oriented lower opening 156 forflow of cold and hot fluids, respectively, through side wall 152. Acircumferential groove 158 within the outer surface of side wall 152 isprovided for a seal 254. A seat 170 is secured to the inner surface ofbottom wall 150 of liner 146 by a screw 172, for seating of a lower edge180 of a side wall 178 of a shuttle 174 and of a biasing spring 188.

The position of shuttle 174 is adjustable within liner 146. Theorientation of sliding movement of shuttle 174 within liner 146 of valvemember 144 defines the major longitudinal axis of valve member 144, andhence of thermostatic mixing valve 102. The upper end of biasing spring188 is transversely restrained (or piloted) by a lower end 198 of aspring pilot 190 having a generally cylindrical shape, and islongitudinally restrained by a flange 192 circumscribing the outersurface or spring pilot 190. Flange 192 is shown in a hexagonalconfiguration to provide wrench flats 200 for threaded assembly to ashuttle 174 and to a relief spring holder 204, shown in FIGS. 4A to 4D.An upper end of spring pilot 190 includes a cavity 194 for the receivingand retaining of the lower end of a relief spring 202. An upper end ofrelief spring 202, and a disc 212 for spreading the axial load of reliefspring 202 upon a lower end of a thermostat 214, is received andretained within a cavity 206 oriented within a lower end of reliefspring holder 204.

In assembly of valve member 144, a first valve member subassembly 240 ismade by inserting disc 212 into cavity 206 within the bottom of reliefspring holder 204, inserting a first end of relief spring 202 intocavity 206 and upon disc 212, placing shuttle 174 upon the bottom ofrelief spring holder 204 so that a second end of relief spring 202projects through an opening 186 within the upper surface of shuttle 134,inserting the second end of relief spring 202 into cavity 194 of springpilot 190, and using wrench flats 200 of spring pilot 190 to fullyengage threads 196 of spring pilot 190 with mating threads 208 withincavity 206 of relief spring holder 204. This secures relief springholder 204, disc 212, relief spring 202, shuttle 174, and spring pilot190 together, with the top surface of shuttle 174 and relief spring 202being clamped between a top surface of cavity 206 of relief springholder 204 and a bottom surface of cavity 194 of spring pilot 190 toform first valve member subassembly 240.

An insert 242 is provided with a seal 246 which is seated within aperipheral groove located near a lower end of insert 242. As shown inFIGS. 3 and 4A through 4D, insert 242 is inserted into an upper end ofliner 146 during assembly of valve member 144, and seal 246 separatescold fluid from hot fluid within valve member 144. Insert 242 includesat least one opening 264 for passage of cold fluid, as shown in FIGS. 3and 4A through 4D. Insert 242 is held in position within a lower portionof bonnet 116 by liner 146, which clamps insert 242 when liner threads160 are engaged with mating threads within an opening 128 of bonnet 116.

Referring again to FIG. 2, seat 170, screw 172, seal 254, insert 242,and seal 246 are preassembled to liner 146, after which biasing spring188 and first subassembly 240 are placed within the open end of liner146. A stem 248 is loosely received within a bellows 222 (shown in FIGS.4A through 4D) of thermostat 214, whereupon thermostat 214 with stem 248is inserted through an opening 210 in a top surface of relief springholder 204 to bear upon disc 212 (contained within first subassembly240).

Valve member 144 is installed to opening 128 in a lower end of bonnet116 using mating threads 160 and 162. A seal 270 seals stem 248 to anaperture 249 within valve cap 134. A second valve member subassembly 250is then formed by further assembling to bonnet 116 a seal 130 and a seal132, valve cap 134 with a seal 136 using threads 138, adjusting screw140, and cover screw 142. Assembly of the thermostatic mixing valve isthen completed by installing second valve member subassembly 250 tocavity 106 of valve body 104 by engaging threads 118 of bonnet 116 withthreads 126 within the opening to cavity 106 of valve body 104.

FIG. 3 shows a plurality of chambers formed within valve body 104 andvalve member 144 of the thermostatic mixing valve. A hot fluid chamber230 is in communication with hot fluid inlet port 112, and a cold fluidchamber 232 is in communication with cold fluid inlet port 110. Both hotfluid chamber 230 and cold fluid chamber 232 are open to valve member144. An inner passage 120 of bonnet 116 includes a preliminary mixingchamber 236, which is in communication with a main mixing chamber 238,which is in turn in communication with a mixed fluid outlet chamber 234,itself in communication with mixed fluid outlet port 114. Inner passage120 and an outer passage 122 of bonnet 116 are separated by an annularinner bonnet wall 266 (which is coupled at a fixed distance from anannular outer bonnet wall 268 by at least two webs 124 (three, or four,are included in any particularly preferred embodiment for structuralrigidity) oriented radially within outer passage 122, having a thicknesssufficient to structurally couple inner bonnet wall 266 to outer bonnetwall 268). Webs 124 are configured with a streamlined cross sectionhaving its greater dimension oriented vertically, in order to minimizeobstruction of flow of mixed fluid.

FIG. 4A–D show a thermostatic control device shown as thermostat 214having a thermostat housing 216 is installed within both preliminarymixing chamber 236 and main mixing chamber 238, which provides a largeheat flow area for thermal convection to, and thermal conductionthrough, the walls of thermostat housing 216. According to aparticularly preferred embodiment, thermostat housing 216 includes atleast one thin wall made of a material having a high coefficient ofthermal conductivity (e.g., a copper alloy) in order to provide a lowthermal impedance to a thermally responsive material 226 containedwithin thermostat housing 216. Thermally responsive material 226 has alarge coefficient of thermal expansion, and therefore expandssubstantially upon increasing in temperature and contracts substantiallyupon decreasing in temperature. Expansion upon increase in temperatureincreases a force exerted upon bellows 222 located within thermostathousing 216.

Various substances are known to those skilled in the art for use asthermally responsive material 226. According to an embodimentparticularly preferred for economy of manufacture, an acetone is usedfor a thermally responsive material. According to an alternativeembodiment particularly preferred for high performance when economy is aless important factor, a halogenated fluorocarbon such as MS-782 VertrelXF manufactured and distributed by Miller-Stephenson Chemical ofDanbury, Conn. is used for a thermally responsive material.

Bellows 222 is constructed in a manner (e.g., using circumferentiallycorrugated metal) which causes it to be radially stiff butlongitudinally flexible. Bellows 222 has a closed end 224 located withinthermostat housing 216, and an open end 220 which is secured to an openend 218 of thermostat housing 216. The periphery of the opening in openend 220 of bellows 222 may be sealed to the open end of thermostathousing 216 to prevent loss of thermally responsive material 226.

Stem 248, of generally cylindrical shape and a diameter which isslightly smaller than is the minimum inside diameter of bellows 222, isplaced within bellows 222 through open end 220. An increase intemperature of thermostat 214, caused by an increase in temperature ofthe mixed fluid surrounding thermostat 214, causes an expansion ofthermally responsive material 226 filling the space between the innersurfaces of thermostat housing 216 and the outer surfaces of bellows222, increasing a longitudinally oriented control force exerted uponclosed end 224 of bellows 222 and thereby upon stem 248, in a directionwhich tends to extend stem 248 out of thermostat 214, and to therebyincrease the combined lengths of thermostat 214 and stem 248.

Upwardly oriented movement of stem 248 is prevented by adjusting screw140 within valve cap 134, so that any motion which occurs will be ofthermostat 214 pressing against either relief spring 202 through disk212 within first subassembly 240 or of thermostat 214 and first assembly240 pressing against biasing spring 188. Relief spring 202 is stiffer(i.e., has a higher spring rate) than is biasing spring 188, soextension of stem 248 out of thermostat 214 results in a displacement ofthermostat 214 vertically downward and an increase in compression ofbiasing spring 188, the compressive force of biasing spring 188balancing the force caused by the expansion of thermally responsivematerial 226 within thermostat 214. Shuttle 174 is thereby displaceddownwardly within liner 146, decreasing open area associated with a hotfluid metering gap 258 of lower opening 156 and consequently flow rateof the hot fluid.

The setpoint temperature to which thermostat 214 controls is primarily afunction of properties of thermally responsive material 226 and force ofbiasing spring 188, which is influenced by the position of adjustingscrew 140. In any particularly preferred embodiment, such designparameters of the valve are selected by the valve designer andmanufacturer so that, in normal operation of the valve using hot andcold fluid sources of typical pressures and temperatures, a desiredmixed fluid outlet temperature can be obtained with adjusting screw 140at or near the center of its range of screw thread travel. Whenadjusting screw 140 is rotated in a clockwise direction (assuming aright-hand thread) to a position farther within valve cap 134, itdecreases the setpoint temperature by reducing the open area of loweropenings 156 and thereby the flow rate of the hot fluid. Conversely,rotating adjusting screw 140 in an opposite direction to a positionnearer the top of valve cap 134 similarly increases the setpointtemperature. Unauthorized tampering with adjusting screw 140 isdiscouraged by concealing adjusting screw 140 beneath a cover screw 142.

Shuttle 174 and liner 146 thus cooperate to function as a hot fluidmetering valve element. Because of the large diameter of the liner,wherein are located flow control openings 156, relative to diameters offlow control openings of the poppet, plug, or globe types of valveelement used in thermostatic control valves prior to the presentinvention, the cumulative open area of lower openings 156 is larger thanis the open area of a comparably nominally sized metering valve of thepoppet, plug, or globe types, allowing a greater amount of flow at anygiven pressure drop through thermostatic mixing valve 102. A smallchange in position of shuttle 174 with respect to liner 146 in apreferred embodiment correspondingly results in a comparably greaterchange in flow rate of hot fluid than does a similar change in positionof a hot fluid flow metering element in a thermostatic mixing valve ofthe poppet, plug, or globe type.

According to a particularly preferred embodiment (by way of example andnot of limitation), of a thermostatic mixing valve, ports 110 and 112are of 1 inch nominal pipe size and 114 is of 1-¼ inch nominal pipesize. Liner 146 is of approximately 1.491/1.492 inch inside diameter.Two lower openings 156 within the wall of liner 146 are spacedapproximately 0.48 inch from two upper openings 154. Each opening 154,156 is configured as a slot cut through the wall of liner 146, subtendsan angle of approximately 145 degrees, and is approximately 0.13 inch inheight, for hot and cold fluid flow areas at liner 146 of approximately0.49 square inch, respectively. Testing of the thermostatic mixing valveusing hot cap water of approximately 160 degrees Fahrenheit (F.) andcold tap water of approximately 55 degrees F. produced the results shownin TABLE 1 below, with a valve shuttle and stem stroked manually andcontrollably. The term “C_(v)” is a measure of valve flow capacity at agiven pressure drop across a valve and is taken from the relationshipQ=C_(v)*(Δp)^(1/2), wherein “Q” designates flow rare in U.S. gallons perminute (gpm) and “Δp” designates pressure drop in pounds per square inch(psi).

TABLE 1 Cold Valve Shuttle And Hot Water Water Cold Flow Stern StrokeFlow Rate Hot Water Flow Rate Water Capacity (inches) (gpm) Δp (psi)(gpm) Δp (psi) (Total C_(v)) 0 4.9 55 51.0 20 12.0 0.0093 11.1 55 48.420 12.3 0.0186 16.6 52 47.1 22 12.3 0.0279 22.7 42 44.5 24 12.6 0.037227.1 35 42.1 26 12.7 0.0465 28.2 30 40.6 28 12.8 0.0558 30.5 25 38.6 3013.1 0.0651 31.7 21 34.9 33 13.0 0.0744 23.9 20 31.1 35 12.8 0.0837 35.916 29.3 40 12.7 0.0930 36.2 14 19.8 45 12.6 0.1023 36.5 11 13.3 50 12.8

The direction of movement of shuttle 174 within liner 146 isperpendicular to that of the fluid being metered, the fluid thereforenot exerting a stagnation or velocity pressure against the face ofshuttle 174 as it does against the flow control element of a poppet,plug, or globe valve. This enables control of higher flow rates athigher velocities and pressures using a smaller thermostat than ispossible with thermostatic valve of the previously used poppet, plug, orglobe types. Liner 146 is closed at its bottom end by a bottom wall 150but has an opening 148 at its upper end, allowing the hot fluid to flowupwardly through the interior of shuttle 174 and passages 182 of shuttle174. Passages 182 are formed by a displacement of a top portion 184 ofshuttle 174 from side wall 178 of shuttle 174, top portion 184 beingheld in fixed relationship to side wall 178 by a web 176 of shuttle 174.

FIG. 3 shows check valve 274 is an installed and operating condition(see FIG. 2 for exploded view). Spring 280 holds plug 282 against seat284 in an absence of flow of mixed fluid from mixed fluid outlet M,fluid pressures being equal on both sides of plug 282 when there is noflow. When mixed fluid M is desired and flow is allowed from mixed fluidoutlet M, back pressure drops on the downstream side of plug 282 andinlet supply pressure forces plug 282 upwardly compressing spring 280 bya distance corresponding to the pressure difference across plug 282.Spring 280 is configured to have a high lateral stiffness, so that itmay not only serve to urge plug 282 against seat 284 but may also guideplug 282 in its path of motion between the opened and closed states ofcheck valve 274.

FIG. 3A is a detail of a portion of check valve 274 shown in FIGS. 2 and3. Stem 286 is provided a tip 286 a of a particular size and shape, andplug 282 is provided a recess 288 which coacts with tip 286 a. These areincluded to maintain the position of plug 282 centrally located withincheck valve 274 during conditions of high flow rate and correspondinglyhigh fluid velocity, When plug 282 is forced fully upward and plug 282,with the associated end of spring 280, may otherwise be dragged towardthe center of thermostatic mixing valve 102 by drag of the high-velocityfluid. (Check valve 274 may also include other associated seals (such asannular seal 283) and washers.) For configuring of check valves 274 foroperation of thermostatic mixing valve 102, the position of threadedstem 286 within check valve cap 276 is adjusted upwardly as shown toprovide plug 282 room to move upward. For service or maintenance ofthermostatic mixing valve 102, stem 286 may be turned to advance itdownwardly and thereby force plug 282 against seat 284 and close off theassociated inlet of thermostatic mixing valve 102.

FIGS. 4A, 4B, 4C, and 4D illustrate the operation of thermostatic mixingvalve 102 in various conditions of operation.

FIG. 4A shows thermostatic mixing valve 102 in normal operation, withshuttle 174 intermediately oriented within liner 146. Cold fluid fromcold fluid inlet port 110 flows through upper opening 154 of liner 146and into preliminary mixing chamber 236, and hot fluid from hot fluidinlet port 112 flows through lower opening 156 of liner 146 and throughan at least one passage 182 of shuttle 174 into preliminary mixingchamber 230. Mixing of the hot and cold fluids begins prior to flowinginto preliminary mixing chamber 236, continues in preliminary mixingchamber 236, and is completed within main mixing chamber 238. Thermostat214 is immersed in the mixed fluid at a particular temperature withinmain mixing chamber 238, and thermally responsive material 226 is atsubstantially the same temperature due to the effects of heat transfer(thermal conduction and convection) at the wall of thermostat housing216. Thermally responsive material 226 will thermostat housing 216, andtherefore bellows 222, are neither fully contacted nor fully expanded,nor is biasing spring 188 fully extended or fully contacted.

In normal operation the temperature of the mixed fluid is controlled bythe longitudinal position of shuttle 174 within and with respect toliner 146, which is in turn controlled by the corresponding specificvolume of thermally responsive material 226 at that temperature and bythe opposing force of biasing spring 188, the latter corresponding tothe position of adjusting screw 140. The open area of a hot fluidmetering gap 258 at lower openings 156, and thereby the rate of flowthrough them, is metered by the longitudinal position of shuttle 174 andthereby by the amount that the side wall 178 of shuttle 174 overlaps andcovers lower openings 156. The flow of hot fluid continues in anupwardly oriented direction into preliminary mixing chamber 236. Hotfluid is kept separated from cold fluid before leaving upper openings154 and lower opening 156 of liner 146 by a shuttle seal 168 orientedwithin a peripherally oriented groove within side wall 173 of shuttle174.

Cold fluid similarly enters valve body 104 through cold fluid inlet port110 and fills cold fluid inlet chamber 232. Cold fluid then flowsthrough transversely oriented openings, shown as upper openings 154,which penetrate the wall of liner 146, and immediately thereafterthrough similarly oriented transverse openings 264 penetrating a wall ofinsert 242. Cold fluid then flows upwardly, meeting and mixing with hotfluid. The at least partially mixed fluid proceeds upwardly throughpreliminary mixing chamber 236 within bonnet inner passage 120 into mainmixing chamber 238, flowing over the surface of thermostat housing 216of thermostat 214 as it does so and thereby maintaining thermallyresponsive material 226 within thermostat housing 216 at a temperaturesubstantially equal to that of the mixed fluid. Mixed fluid then flowsdownwardly through an outer bonnet passage 122 into a mixed fluid outletchamber 234, from which it exits the thermostatic ring valve throughmixed fluid outlet port 114.

FIG. 4B shows a condition of operation in which the mixed fluid hasbecome too hot (e.g. caused by a large increase in temperature or supplypressure of the hot fluid) and thermally responsive material 226 hastherefore expanded. This has forced thermostat 214, and thereby loweredge 180 of side wall 178 of shuttle 174, downward onto seat 170,completely covering lower openings 156 to decrease the hot fluidmetering gap to substantially zero and substantially stopping flow ofhot fluid. Because lower edge 180 is now abutting seat 170, biasingspring 188 can be compressed no farther. To prevent thermostat housing216 and/or bellows 222 from rupturing due to excessive expansion ofthermally responsive material 226 caused by excessively high temperatureof the mixed fluid, relief spring 202 allows additional extension ofstem 248 from thermostat 214 by compressing in response to the expansionof thermally responsive material 226, thus relieving excessive forceotherwise exerted by thermally responsive material 226.

FIG. 4C shows a condition of operation in which the temperature of themixed fluid has become too cold (e.g., caused by a large reduction intemperature and/or supply pressure of the hot fluid). Thermallyresponsive material 226 has cooled in response to the reducedtemperature of the mixed fluid surrounding thermostat 214, and hascontracted and has reduced the force it exerts upon biasing spring 188through thermostat 214 and first assembly 240. This allows biasingspring 188 to lift first subassembly 240 and thermostat 214, maintainingthe abutting relationship between stem 248 and adjusting screw 140.Shuttle 174 is a member of first subassembly 240, and is thereforelifted with it, increasing the hot fluid metering gap of lower openings156 fully. Hot fluid flow rate thereby increases and relieves theexcessively cold condition of the mixed fluid, bringing valve member 144back into equilibrium.

FIG. 4D shows an abnormal condition of operation which is encounteredwhen thermostat 214 fails to function, in the illustrated instance dueto leakage of thermally responsive material 226 through a rupture inbellows 222. Since thermostat 214 is now unable to retain thermallyresponsive material 226 within housing 216, spring 188 forces thermostat214 and first subassembly 240 upward until stopped by abutting of a topsurface of top portion 184 of shuttle 174 upon a lower surface, or anauxiliary seat 260, of insert 242. Although this fully opens loweropenings 156 for maximum flow rate of hot fluid, the abutting of shuttle174 top portion 184 upon auxiliary seat 260 constitutes closure of abackup shutoff valve 272 and prevents hot fluid from flowing beyondshuttle 174 into preliminary mixing chamber 236. Cold fluid, however,continues to flow unimpeded and unabated. Therefore, a failure ofthermostat 214 results in a condition of an emergency shower bathremaining available (with cold fluid only) in spite of a failure ofthermostat 214.

FIGS. 5 through 10 show an alternative embodiment of the thermostaticmixing valve for the producing of a mixed fluid of a particulartemperature from a cold fluid and a hot fluid, wherein all flow (i.e.,flow of the cold fluid, the hot fluid, and mixed fluid) is stopped uponfailure of the thermostatic control device (e.g., shown as a devicewhich changes in length upon a change in temperature of a fluid in whichthe device is at least partially immersed).

FIGS. 5 and 6 show the alternative embodiment of a thermostatic mixingvalve 302 including a valve body 304 having a cold fluid inlet port 310and a hot fluid inlet port 312 (given reference letters C and H,respectively) and a single mixed fluid outlet port 314 (given areference letter M). Ports 312, 310, and 314 are configured for sealablyconnecting fluid conduits (e.g., using pipe threads). A valve cap 334 ismounted upon the top of valve body 304, and holds an adjusting screw 340and a cover screw 342, both shown in FIG. 7. Thermostatic mixing valve302 further includes a first check valve 474 associated with hot fluidinlet H and a second check valve 474 associated with cold fluid inlet C,each check valve 474 including a check valve cap 476 in which isthreadedly engaged a stem 486.

Valve body 304, valve cap 334, adjusting screw 340, and cover screw 342may be made of various materials. According to any preferred embodiment,valve body 304 and valve cap 334 are cast of brass, gray iron, orductile iron, and adjusting screw 340 and cover screw 342 are machinedof brass, bronze, or stainless steel.

FIG. 7 shows valve body 304, valve cap 334, a thermostat 414, thermostatadjusting screw 340 and cover screw 342, a cold fluid inlet chamber 432and a hot fluid inlet chamber 430, a main mixing chamber 438, and afluid flow control element shown as a valve member 344. Hot fluid inletport 312 and cold fluid inlet port 310 are oriented near the right andleft sides of the valve respectively, and mixed fluid outlet port 314 islocated at the bottom of valve body 304 and is open to a mixed fluidchamber 434. Valve body 304 further includes a cavity 306, open at itstop for the receiving of a valve member 344.

A check valve (shown as check valve 474) is assembled to valve body 304in association with each inlet port 310 and 312. Check valve 474includes a seat 484, a plug 482, a check valve cap 476, a stem 486, acylindrical filter screen 479 (with a centering taper), and a biasingspring 480. Check valve cap 476 is provided with threads 494 forengagement with a threaded aperture 496 within valve body 304, and issealed to valve body 304 with an annular seal 478. Stem 486 is providedwith treads 490 for engagement with a threaded aperture 492 centrallylocated within check valve cap 476, and is sealed to check valve cap 476by an annular seal 485. Spring 480 holds plug 482 against seat 484 in anabsence of flow of mixed fluid from mixed fluid outlet M, fluidpressures being equal on both sides of plug 482 (which may have atapering shape and may be provided with one or more annular seals) whenthere is no flow. When mixed fluid M is desired and flow is allowed frommixed fluid outlet M, back pressure drops on the downstream side of plug482 and inlet supply pressure forces plug 482 downward, compressingspring 480 by a distance corresponding to the pressure difference acrossplug 482. Spring 480 is configured to have a high lateral stiffness, sothat it may not only serve to urge plug 482 against seat 484 but mayalso guide plug 482 in its path of motion between the opened and closedstates of check valve 474.

FIG. 7A is a detail of a portion of check valve 474 shown in FIG. 7.Biasing spring 480 is a compression coil spring, and is engaged withcheck valve cap 476 by a special thread 481 upon check valve cap 476having a thread form, pitch, and pitch diameter matching theconfiguration of biasing spring 480. Biasing spring 480 is similarlyengaged with plug 482 by a similar thread 471. For configuring of checkvalves 474 for operation of thermostatic mixing valve 302, the positionof threaded stem 486 within check valve cap 476 is adjusted downwardlyas shown to provide plug 482 room to move downward. For service ormaintenance of thermostatic mixing valve 302, stem 486 may be turned toadvance it upwardly and thereby force plug 482 against seat 484 andclose off the associated inlet of thermostatic mixing valve 302.

Valve body 304 is divided into various chambers including a main mixingchamber 438 (of an annular shape, oriented below valve cap 334), a coldfluid chamber 432 (of an annular shape, and in communication with coldfluid inlet port 310), a hot fluid chamber 430 (of an annular shape, andin communication with hot fluid inlet port 312), and mixed fluid outletchamber 434 in communication with mixed fluid outlet port 314. Valvemember 344 is installed within cavity 306 of valve body 304 and issecured within valve body 304 by engagement of a screw thread 360 uponvalve member 344 with a screw thread 308 within cavity 306. Apreliminary mixing chamber 436 (also shown in FIG. 8) is containedwithin valve member 344, as is a shuttle 374 for modulating flows of hotand cold fluid (shown in FIGS. 8 and 10).

Referring to FIG. 9, which is a partially exploded view of thermostaticmixing valve 302, valve body 304 is shown with valve member 344 andvalve cap 334. Valve member 344 is generally cylindrical in shape and isinstalled within generally cylindrical valve body cavity 306 inside ofvalve body 304. A threaded portion 360 of a liner 346 of valve member344 is engaged with a lower threaded bore 308 within cavity 306 tosecure valve member 344 within valve body 304. A upper liner seal 452and a lower liner seal 454 prevent leakage. Valve cap 334 has a threadedportion 338 that is threaded into an upper threaded bore 326 of valvebody 304 to secure valve cap 334 to valve body 304 and to close valvebody cavity 306. Valve cap 334 holds adjusting screw 340, the positionof which is secured against tampering by cover screw 342. Adjustingscrew 340 and cover screw 342 are engaged with screw threads locatedwithin an upper area of an aperture 427 extending through valve cap 334,and an upper portion of thermostat 414 is installed with a lower portionof aperture 427 so that it bears upon the bottom of adjusting screw 340.A seal 428 seals thermostat 414 to aperture 427 within valve cap 334,while a seal 336 seals valve cap 334 to valve body 304.

Valve member 344 includes cylindrical liner 346 and thermostat 414having a cylindrical thermostat housing 416 that is at least partiallyreceived within the interior of valve cap 334 when valve cap 334 isthreaded onto valve body 304. Valve member 344 further includes a topflange 364 which includes a hub 362 (shown with a hexagonal shape tofacilitate installation with a wrench) having a central circular opening348 within which thermostat housing 416 freely slides. Cylindrical liner346 of valve member 344 includes two sets of circumferentially orientedopenings (shown as upper openings 354 and lower openings 356) which formpassages through a side wall 352 of liner 346.

Valve member 344 is shown in an exploded view of FIG. 10 so that therelationship of its elements may be more clearly described.

Thermostat 414, having a thermostat housing 416, is installed withinboth preliminary mixing chamber 436 and main mixing chamber 438.According to a particularly preferred embodiment, thermostat housing 416includes at least one thin wall made of a material having a highcoefficient of thermal conductivity (e.g., a copper alloy) in order toprovide a low thermal impedance from the mixed fluid to a thermallyresponsive material 226 (e.g. acetone) contained within thermostathousing 416 and thereby shorten response time of thermostatic mixingvalve 302. Thermally responsive material 226 has a large coefficient ofthermal expansion, and therefore expands substantially upon increasingin temperature and contracts substantially upon decreasing intemperature. Expansion of thermally responsive material 226 withinthermostat housing 416 upon an increase in temperature increases a forceexerted upon bellows 422 located within thermostat housing 416.

Bellows 422 is constructed in a manner (e.g., using circumferentiallycorrugated metal) which causes it to be radially stiff butlongitudinally flexible. Bellows 422 is hollow and has a first end 424which is closed and located within thermostat housing 416, and a secondend 420 which is open and secured to an open end 418 of thermostathousing 416. Bellows 422 is installed to an open end 418 of housing 416and is sealed thereto by a seal 462. A valve stem 448 (e.g., acylindrical rod) extends through an opening in a second end 420 and intobellows 422 so that the upper end of stem 448 bears upon the innersurface of the first end 424 of bellows 422, and is maintained in thisbearing relationship by a compressive coil biasing spring 388 pressingupon the lower end of stem 448 through a transversely oriented web 376of shuttle 374, a relief spring 402, and a disc 412. Shuttle 374, havinga cylindrical shape, is slidably received within liner 346 and isprovided a seal 368 for sealing cold fluid from hot fluid. Theorientation of sliding movement of shuttle 374 and of stem 448 definesthe major longitudinal axis of valve member 344, and hence ofthermostatic mixing valve 302. Shuttle 374 includes a side wall 378 anda spring pilot portion 390. Side wall 378 is joined to spring pilotportion 390 by a transversely oriented and ring-shaped web 376 having atleast one passage 382 through which fluid flows in an axial direction.Spring pilot portion 390 of shuttle 374 has a closed bottom 398 and anopen top with a threaded bore (visible in FIG. 8) which is used toassemble a top portion 384 of shuttle 374, a relief spring 402 beingretained within a relief spring holder 404, configured as a cavitywithin spring pilot 390, by top portion 384 of shuttle 374. As shown inFIGS. 8 and 10, an annular space 391 exists between an outer surface ofspring pilot portion 390 and an inner surface of side wall 378 ofshuttle 374.

Thermally responsive material 226, expanding or contracting withinthermostat housing 416 generally in correspondence to an increase ordecrease respectively in temperature of the mixed fluid surroundingthermostat housing 416, causes bellows 422 to contract and expandcorrespondingly and respectively, in opposition to biasing spring 388.Stem 448, in contact with bellows 422, is thereby moved tocorrespondingly adjust longitudinal position of shuttle 374, which iscoupled to stem 448, within liner 346 and to thereby proportionallyregulate the sectional flow areas of a cold fluid metering gap 456 and ahot fluid metering gap 458, and thereby the temperature of the mixedfluid. Adjusting screw 340 changes the force exerted by biasing spring388 by shifting position of the group of parts including thermostat 414,stem 448, shuttle 374, disc 412, and relief spring 402, therebyadjusting temperature of the mixed fluid within main mixing chamber 438at which shuttle 374 reaches a particular position within liner 346.

The setpoint temperature, or temperature to which thermostat 414controls is primarily a function of properties of thermally responsivematerial 226 and force of biasing spring 388, which is influenced by theposition of adjusting screw 340. In any preferred embodiment, suchdesign parameters of the valve are selected by the valve designer andmanufacturer so that, in normal operation of the valve using hot andcold fluid sources of typical pressures and temperatures, a desiredmixed fluid outlet temperature can be obtained with adjusting screw 340at or near the center of its range of screw thread travel. Whenadjusting screw 340 is rotated in a clockwise direction (assuming aright-hand thread) to a position farther within valve cap 334, itdecreases the setpoint temperature by reducing the open area of loweropening 356 and thereby the flow rate of the hot fluid. Conversely,rotating adjusting screw 340 in an opposite direction to a positionnearer the top of valve cap 334 similarly increases the setpointtemperature. Concealing adjusting screw 340 beneath a cover screw 342discourages unauthorized tampering with adjusting screw 340.

Shuttle 374 and liner 346 thus cooperate to function as a fluid meteringvalve element. Because of the large diameter of the liner, wherein arelocated flow control openings 356, relative to diameters of flow controlopenings of the poppet, plug, or globe types of valve element, thecumulative open area of lower openings 356 is larger than is the openarea of a comparably nominally sized metering valve of the poppet, plug,or globe types, allowing a greater amount of flow at any given pressuredrop through thermostatic mixing valve 302. A small change in positionof shuttle 374 with respect to liner 346 in any preferred embodimentcorrespondingly results in a comparably greater change in flow rate ofhot fluid than does a similar change in position of a hot fluid flowmetering element in a thermostatic mixing valve of the poppet, plug, orglobe type.

The direction of movement of shuttle 374 within liner 346 isperpendicular to that of the fluid being metered, the fluid thereby notexerting a stagnation or velocity pressure against the face of shuttle374 as it does against the flow control element of a poppet, plug, orglobe valve. This enables control of higher flow rates at highervelocities and pressures using a smaller thermostat than is possiblewith thermostatic valve of the previously used poppet, plug, or globetypes.

Valve member 344 includes a top shuttle portion 384 having a centralcircular opening 386. Valve stem 448 is inserted at its lower endthrough opening 386 and abuts disc 412, which provides an enlarged areaupon which relief spring 402 bears. Disc 412 and relief spring 402 areinstalled within spring pilot portion 390 of shuttle 374, and aresecured therein by top portion 384 of shuttle 374 when it is installedto spring pilot 390 portion by, e.g., screw threads. The lower end ofvalve stem 448 extends slidably through the central circular opening 386within top portion 384, and is maintained in contact with disc 412 bybiasing spring 388.

Liner 346 is provided a bottom wall 350, which is configured as aseparate part although it may alternatively be made integral with liner346. As shown, bottom wall 350 is a threaded plug having a centralinterior recess 366 for seating of biasing spring 388. Bottom wall 350also includes a seat 370 for seating of a bottom edge 380 of outer wall378 of shuttle 374. Biasing spring 388 is seated at its upper end uponring-shaped web 376 and around the perimeter of spring pilot 390 portionof shuttle 374.

Operation of thermostatic mixing valve 302 is described below inreference to FIGS. 8A through 8D.

FIG. 8A shows thermostatic mixing valve 302 in normal operation, withshuttle 374 intermediately oriented within liner 346. Cold fluid fromcold fluid inlet port 310 flows through upper openings 354 within sidewall 352 of liner 346, and hot fluid from hot fluid inlet port 312 flowsthrough lower openings 356 within side wall 352 of liner 346 and throughpassages 382 of shuttle 374. Mixing of the hot and cold fluids beginsimmediately, continues in preliminary mixing chamber 436, and iscompleted as the at least partially mixed fluids enter main mixingchamber 438. Thermostat 414 is immersed in the mixed fluid at aparticular temperature within main mixing chamber 438, and thermallyresponsive material 226 is at substantially the same temperature due tothermal convection at the wall of housing 416 and thermal conductionthrough the wall of housing 416. Thermally responsive material 226within thermostat housing 416, and therefore bellows 422, are neitherfully contracted nor fully expanded, nor is biasing spring 388 fullycontracted or fully extended. In normal operation, the temperature ofthe mixed fluid is controlled by axial position of shuttle 374 withinand with respect to liner 346, which is in turn controlled by thecorresponding specific volume of thermally responsive material 226 atthat temperature and by the opposing force of biasing spring 388, thelatter corresponding to the position of adjusting screw 340.

In FIG. 8B, the valve is shown compensating for a hot outlet fluidcondition (with respect to the temperature setting). Shuttle 374 isoriented fully downward (at the end of its normal axial path of travel)within liner 346 because thermally responsive material 226 has expandedand bellows 422 has therefore contracted, thereby moving shuttle 374downwardly.

Were the mixed fluid to be still hotter, thermally responsive material226 would attempt to expand further and, if stem 448 were blockedagainst further movement downward, thermally responsive material 225could expand to the point that damage could result to housing 416,bellows 422, or the junction of bellows 422 with housing 416. To preventthis from happening, relief spring 402 provides for additional movementof stem 448 when shuttle 374 is blocked by seat 370 of bottom wall 350against further movement, thereby relieving force otherwise caused byexcessive expansion of thermally responsive material 226. Lower openings356 within side wall 352 of liner 346 are closed, blocked by side wall378 or shuttle 374. The bottom edge 380 of side wall 378 of shuttle 374rests against the top of seat 370 of bottom wall 350, and side wall 378of shuttle 374 closes lower openings 356, reducing hot fluid meteringgap 458 to substantially zero which substantially prevents the flow ofhot fluid into preliminary mixing chamber 436. Cold fluid flows throughupper openings 354 of liner 346 and into preliminary mixing chamber 436(above shuttle 374). The temperature of the mixed fluid in main mixingchamber 438 thus decreases because the flow from cold fluid inletchamber 432 is in greater proportion of the total flow than it had been.As the temperature of the mixed fluid decreases, causing thermallyresponsive material 226 to contract, bellows 422 expands, readjustingthe position of shuttle 374 and bringing the temperature of the mixedfluid into an equilibrium condition with respect to the temperaturesetting of the valve.

In FIG. 8C, the valve is shown compensating for a cold fluid condition(with respect to the temperature setting of the valve). Shuttle 374 isoriented upwardly (at the end of its normal axial path of travel asconstrained by valve stem 448 within bellows 422) within liner 346because thermally responsive material 226 has contracted, allowingbellows 422 to expand and thereby allowing biasing spring 388 to expand(within a constrained axial path of travel defined by valve stem 448within bellows 422 of thermostat 414). Upper openings 354 of liner 346are closed, blocked by side wall 378 of shuttle 374, which reduces coldfluid metering gap 456 to substantially zero and thereby substantiallyprevents the flow of cold fluid into preliminary mixing chamber 436. Hotfluid flows through lower openings 356 of liner 346 and into preliminarymixing chamber 436 (through passages 382 within shuttle 374). Thetemperature of the mixed fluid in main mixing chamber 438 thus increasesbecause the flow from hot fluid chamber 430 is in greater proportion ofthe total flow than it had been. Bellows 422 thereafter contracts as thetemperature of the mixed fluid, and of thermally responsive material226, increases, readjusting the position of shuttle 374 and therebybringing the temperature of the mixed fluid into an equilibriumcondition with respect to the temperature setting of the valve.

In FIG. 8D, thermostatic mixing valve 302 is shown in a failurecondition caused by rupture of bellows 422 within thermostat housing416. Biasing spring 388 has fully expanded (no longer constrained bybellows 422, see FIG. 8C), driving shuttle 374 upward and therebyforcing disc 412 into valve stem 448 and driving top portion 384 ofshuttle 374 fully upward into an auxiliary seat 460, effectively forminga backup shutoff valve 472 within thermostatic mixing valve 302. Whilehot fluid flows through lower openings 356 of liner 346 and through atleast one shuttle passage 382 up into preliminary mixing chamber 436, itis prevented from flowing beyond preliminary mixing chamber 436 and intomain mixing chamber 438 by the engagement of upper portion 384 withauxiliary seat 460. Moreover, upper openings 354 of liner 346 areblocked by side wall 378 of shuttle 374 to shut off flow of cold fluid.The seating of top portion 384 upon auxiliary seat 460 blocks all flowfrom preliminary mixing chamber 436 to main mixing chamber 438 bybiasing spring 388. Consequently, no fluid (hot, cold, or mixed) flowsthrough outlet port 314.

As shown in the embodiments of FIGS. 1–3 and 5–7, valve body 104, 304includes a third fluid inlet 510 positioned between the check valve seat284, 484 and the mixed fluid outlet port 114, 314. Illustratively, thethird fluid inlet port 510 is between the cold fluid inlet port 110, 310and the mixed fluid outlet port 114, 314. Further illustratively, in theembodiment of FIG. 3, third fluid inlet 510 is adjacent to plug 282. Asshown in FIGS. 3 and 7, third fluid inlet 510 is illustratively betweenthe mixing chamber 238, 438 and check valve seat 284, 484.

Although only a few exemplary embodiments of the present invention havebeen described in detail, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. For example, valve caps may be secured tovalve bodies by machine screws; bellows may be brazed or soldered tothermostat housing walls or bases to form substantially hermetic seals.Accordingly, all such modifications are intended to be included withinthe scope of the invention as defined in the following claims. In theclaims, each means-plus-function clause is intended to cover thestructures described herein as performing the recited function, and notonly structural equivalents but also equivalent structures. Othersubstitutions, modifications, changes, and omissions may be made in thedesigns, operating conditions, and arrangements of the preferredembodiments without departing from the spirit of the invention asexpressed in the appended claims.

1. A mixing valve comprising: a valve body formed to include a hot fluidinlet, a cold fluid inlet, a third fluid inlet, a mixed fluid outlet, afirst chamber for receiving cold fluid from the cold fluid inlet andthird fluid from the third fluid inlet, and a mixing chamber positionedto receive fluid from the first chamber and the hot fluid inlet anddischarge a mixture of the received hot, cold, and third fluids from themixing chamber via the mixed fluid outlet port, a thermostat to sensethe temperature of fluid in the mixing chamber and move a valve memberin response to changes in the temperature of fluid in the mixingchamber, the third fluid inlet positioned relative to the cold fluidinlet to permit fluid to flow through the third fluid inlet and mix withthe fluid from the cold fluid inlet in the first chamber prior to beingreceived by the mixing chamber.
 2. The mixing valve of claim 1, whereinthe third fluid inlet is positioned relative to the cold fluid inlet topermit third fluid to flow through the third fluid inlet into a coldfluid chamber in a direction substantially transverse to the directionof cold fluid flows through the cold fluid inlet.
 3. The mixing valve ofclaim 1, further comprising a check valve, wherein the third fluid inletis positioned downstream of the check valve so that, when the checkvalve is in a closed orientation, the flow of fluid through the coldfluid inlet is substantially obstructed, and the third fluid inlet issubstantially unobstructed.
 4. The mixing valve of claim 1, wherein thethird fluid inlet is positioned so that fluid flows from the third fluidinlet in a direction that is substantially transverse to the directionof movement of the valve member.
 5. The mixing valve of claim 4, whereinthe third fluid inlet is positioned relative to the cold fluid inlet topermit fluid to flow through the third fluid inlet into a cold fluidchamber in a direction substantially transverse to the direction inwhich cold fluid flows through the cold fluid inlet.
 6. The mixing valveof claim 3, wherein the check valve includes a check valve membermovable between a position engaging a seat to restrict flow of fluidpast the seat to a position permitting flow of fluid past the seat, andthe third fluid inlet is positioned so that fluid flows from the thirdfluid inlet in a direction that is substantially transverse to thedirection of movement of the check valve member.
 7. The mixing valve ofclaim 6, wherein the third fluid inlet is positioned relative to thecold fluid inlet to permit fluid to flow through the third fluid inletinto a cold fluid chamber in a direction substantially transverse to thedirection in which cold fluid flows through the cold fluid inlet.
 8. Themixing valve of claim 1, further comprising a cap, and the third fluidinlet is an opening formed in the valve body and is sized to receive thecap when the third fluid inlet is not in use.
 9. The mixing valve ofclaim 8, wherein the cap and the opening are complementarily threaded.10. The mixing valve of claim 2, further comprising a threaded cap, andthe third fluid inlet is an opening formed in the valve body and iscomplementarily threaded and sized to receive the cap when the thirdfluid inlet is not in use.
 11. A method of mixing fluids comprising:providing a valve body formed to include a hot fluid inlet, a cold fluidinlet, a third fluid inlet adjacent the cold fluid inlet, and a mixingchamber positioned to receive fluid from the hot, cold, and third fluidinlets, the valve body further comprising a thermostat positioned atleast partially in the mixing chamber to sense the temperature of amixture of the fluids received via the hot, cold, and third inlets inthe mixing chamber and move a valve member in response to changes in thetemperature of fluid in the mixing chamber, and introducing a thirdfluid via the third fluid inlet and introducing cold fluid via the coldfluid inlet into a cold fluid chamber to permit blending of cold fluidand third fluid.
 12. The method of claim 11, wherein the valve body isformed to include a third fluid inlet positioned relative to the coldfluid inlet to permit fluid to flow through the third fluid inlet intothe cold fluid chamber in a direction substantially transverse to thedirection of cold fluid flows through the cold fluid inlet.
 13. Themethod of claim 11, wherein the valve body is formed to include a thirdfluid inlet, the valve body further comprising a check valve in the coldfluid inlet, wherein the third fluid inlet is positioned downstream ofthe check valve so that, when the check valve is in a closedorientation, the flow of fluid through the cold fluid inlet issubstantially obstructed, and the third fluid inlet is substantiallyunobstructed.
 14. The method of claim 13, wherein the third fluid inletis positioned relative to the cold fluid inlet to permit fluid to flowthrough the third fluid inlet into the cold fluid chamber in a directionsubstantially transverse to the direction in which cold fluid flowsthrough the cold fluid inlet.
 15. The method of claim 13, wherein thecheck valve includes a check valve member movable between a positionengaging a seat to restrict flow of fluid past the seat to a positionpermitting flow of fluid past the seat, and the third fluid inlet ispositioned so that fluid flows from the third fluid inlet in a directionthat is substantially transverse to the direction of movement of thecheck valve member.
 16. The method of claim 15, wherein the third fluidinlet is positioned relative to the cold fluid inlet to permit fluid toflow through the third fluid inlet into the cold fluid chamber in adirection substantially transverse to the direction in which cold fluidflows through the cold fluid inlet.
 17. The method of claim 12, furthercomprising providing a cap, and the third fluid inlet is an openingformed in the valve body and is sized to receive the cap when the thirdfluid inlet is not in use.
 18. The method of claim 17, wherein the capis complementarily threaded with complementary threads formed at theopening.
 19. The method of claim 12, further comprising providing athreaded cap, and the third fluid inlet is an opening formed in thevalve body and is complementarily threaded and sized to receive the capwhen the third fluid inlet is not in use.
 20. A system for mixing fluidscomprising: a mixing valve and a fluid conducting network, the mixingvalve including a mixed fluid outlet, a hot fluid inlet, a cold fluidinlet, a third fluid inlet adjacent the cold fluid inlet, a firstchamber for receiving cold fluid from the cold fluid inlet and thirdfluid from the third fluid inlet, and a mixing chamber positioned toreceive fluid via the first chamber and the hot fluid inlet, a valvemember to adjust the amount of fluid flowing through at least one of thehot and the cold fluid inlets, and a thermostat to move the valve memberin response to changes in temperature of the fluid adjacent thethermostat, the fluid conducting network coupled to the mixing valve andincluding a hot fluid supply line to supply hot fluid to the hot fluidinlet of the mixing valve, a cold fluid supply line to supply cold fluidto the mixing valve, a mixed water line coupled to the mixed fluidoutlet, and a recirculation line coupled between the mixed water lineand the third fluid inlet to permit flow of third fluid to the mixingvalve via the third fluid inlet.